1. Field of the Invention
The present invention relates to a functional film, and more particularly, to a functional film having excellent contrast and antistatic characteristics and capable of providing a high quality of picture and a good body color, and a cathode ray tube (CRT) adopting the same.
2. Description of the Related Art
FIG. 1 is a sectional view of a general CRT. As shown in FIG. 1, the general CRT includes a panel 11, a fluorescent layer 12 formed inside the panel 11 with a predetermined pattern, a shadow mask frame assembly 13 installed inside the panel 11, and a funnel 14 having a cone portion 14a and a neck portion 14b forming a bulb of the CRT which is attached to the panel 11. Here, a deflection yoke 15 is installed around the cone portion 14a and an electron gun 16 is inserted in the neck portion 14b.
Here, a curved panel having a predetermined curvature is generally used as the panel. However, a problem of having a curved panel is that dazzling and distortion of the picture become serious at the outer area of the panel, so it is difficult to display a high quality picture.
In order to make up for the problem, a panel having an infinite curvature, i.e., a planar panel, has been suggested.
The larger the curvature is, that is, the flatter the panel is, the more the dazzling, caused by reflection of external light, is suppressed, so a distinct picture can be obtained without distortion of the picture and eye strain.
FIG. 2A shows an example of a planar panel, in which the inner and outer surfaces of the panel are both planar. However, in a case where a cathode ray tube (CRT) adopts such a panel, the picture is seen to be apparently compressed at the center of the panel.
To solve this problem, a planar panel having a flat outer surface and a curved inner surface having a predetermined curvature, as shown in FIG. 2B, has been suggested.
However, the planar panel having the above structure has a problem in that transmission is different at the center and the peripheral areas due to the difference in thickness. Further, if the planar panel having the above structure is applied to a generally used dark tint or semi tint panel of which transmission is 40.about.50%, the difference in transmission at the center and peripheral areas of the panel increases. As a result, it is difficult to obtain a uniform quality of picture. Thus, a clear tint panel having a transmission of 80% or more is usually adopted.
However, reflection of external light becomes serious as the transmission of the panel increases, thereby lowering contrast. That is, if external light is incident, an afterimage is formed on the outer surface of the panel, so that the picture displayed on the inner surface of the panel overlaps with the afterimage, thereby lowering contrast.
Also, another problem of the planar panel is that subillumination occurs at regions where each color overlaps when a fluorescent body is illuminated, thereby lowering the purity and range of color reproduced.
In addition, a common problem of the CRT is the accumulation of charge before and after the operation of the CRT at the outer surface of the panel, and hence generation of static electricity. When static electricity is generated, dust sticks to the outer surface of the panel, thereby deteriorating the appearance. Also, in some cases, an operator may be electrically shocked by the static electricity.
As a method capable of overcoming the above-described various problems, a dispersion, obtained by dispersing conductive particles such as antimony-doped tin oxide (ATO) or indium tin oxide (ITO) in silicate, is applied to the outer surface of the panel. However, this method does not sufficiently prevent reflection of the external light even though it can enhance the antistatic characteristics. Thus, dazzling and purity of color are not still improved.
Another method is to directly sputter a high refractive material and a low refractive material onto the external surface of the panel in turn using a sputtering method or a chemical vapor deposition (CVD) method such that a layer made of a material having a high refractive index (hereinafter, refer to a high refractive layer) and a layer made of a material having a low refractive index (hereinafter, refer to a low refractive layer) are alternately formed. According to this method, reflection of the external light caused by interference and electromagnetic shielding are prevented. However, this method cannot provide an improvement in the purity of color, and requires very expensive equipment.
Still another method is to attach a film to the external surface of a glass panel, and the present invention relates to this method.